The present invention relates to molded PTFE articles for use as containers for high purity chemicals, typically in the area of semiconductor manufacturing, or as a lining material for transport pipes.
Because of the excellent heat and chemical resistance of polytetrafluoroethylene (hereafter PTFE) and modified polytetrafluoroethylene, articles formed from these polymers are extensively used in transport pipes that handle corrosive or high temperature fluids or as corrosion resistant lining material for tanks, machines, equipment, and the like.
However, generally, the surface of PTFE molded articles is not sufficiently smooth. This is a cause for concern when such articles are used as containers for high purity chemicals or linings for transport pipes, since contaminants tend to adhere to the surface and are difficult to remove even after attempts are made to clean the articles. In particular, the removal of contaminants has become a rigorous requirement in areas requiring sophisticated physical properties, particularly in semiconductor fabrication or the like.
The present invention provides for a molded article of polytetrafluoroethylene or modified polytetrafluoroethylene having a fluoropolymer resin coating, the coating comprising a heat-flowable tetrafluoroethylene copolymer wherein the surface of the coated article has a reduced roughness as compared to the molded article prior to coating. The coating for the molded article is preferably a fused powder, most preferably formed by electrostatically applying a fluoropolymer powder resin to the molded PTFE article. In a preferred embodiment the fluoropolymer powder resin comprises a mixture of heat-flowable tetrafluoroethylene copolymer powder and a polytetrafluoroethylene powder that has a temperature of crystallization of at least 305xc2x0 C. and a heat of crystallization of at least 50 J/g.
The invention further provides for a process for forming a smooth surface on a molded article of polytetrafluoroethylene or modified polytetrafluoroethylene by coating the article with a heat-flowable fluoropolymer powder resin and heating the coated article to form a fused fluropolymer resin coating wherein the surface of the coated article has a reduced roughness compared to the molded article prior to coating.